The disclosure relates to a reactive power compensation apparatus and a control method thereof.
As industries are developed and population increases, power demand rapidly increases. On the other hand, there is a limit to power production.
Accordingly, power systems for stably power generated from production areas to demand areas without loss gradually become important.
The necessity of a Flexible AC Transmission System (FACTS) for improving power flow, voltage of the power system, and stability comes to the fore. In the FACTS, a STATic synchronous COMpensator (STATCOM) that is one of third-generation reactive power compensation apparatuses is synchronized with a power system to compensate for reactive power required by the power system.
FIG. 1 illustrates a general power system.
As shown in FIG. 1, the general power system 10 may include a power generation source 20, a power system 30, a load 40, and a plurality of reactive power compensation apparatuses 50.
The power generation source 20 refers to a place or facility that generates power, and may be understood as a producer that generates power.
The power system 30 may refer to an integrated facility including power lines, steel transmission towers, arresters, insulators, and the like, which allow power generated from the power generation source 20 to be transmitted to the load 40.
The load 40 refers to a place or facility that consumes power generated from the power generation source 20, and may be understood as a consumer that consumes power.
The reactive power compensation apparatus 50 is a STATCOM, and is associated with the power system 30 to compensate for reactive power flowing through the power system 30 when the reactive power is insufficient.
The reactive power compensation apparatus 50 includes a converter capable of converting AC power into DC power or converting DC power into AC power.
The converter includes a cluster including a plurality of cells connected in series for each of three phases.
FIG. 2A is a circuit diagram of a converter having a star connection topology, and FIG. 2B is a circuit diagram of a converter having a delta connection topology.
As shown in FIGS. 2A and 2B, each converter has a structure in which a plurality of cells 54 are connected in series in each of three-phase clusters 52.
Each cell is provided with a bypass switch, so that, although a corresponding cell is faulty, the corresponding cell is bypassed by the bypass switch. Thus, the remaining cells except for the faulty cell are normally available, and accordingly, the converter can be normally operated.
As shown in FIG. 3A, when numbers of cells included in the respective phases are equal to one another, voltages of the respective phases, i.e., total voltages of the cells included in the respective phases are equal to one another, and thus the voltages of the respective phases make balance. Hence, the voltages of the respective phases can be equally controlled.
However, as shown in FIG. 3B, when some cells among the cells included in a specific phase, e.g., phase are faulty or eliminated, a total voltage of cells included in the phase c becomes smaller than that of cells included in phase a or b. Hence, voltages of the respective phases are unbalanced, and therefore, it is difficult to equally control the voltages of the respective phases.